The present invention relates to the connection of reactant gas plenums or manifolds to individual stacks of fuel cells used in the production of electrical energy from gaseous fuels. The invention is particularly directed to electrically insulative sealing members for interpositioning between the cell stack and the reactant gas supply.
In an effort to develop new sources of electrical power, fuel cells have received considerable study and development effort. Individual cells of relatively low electrical potential and capacity are arranged in large fuel cells stacks. Several fuel cell stacks may be combined in a module or assembly within a single containment vessel for manufacture and shipping to a power plant site.
The individual stacks of fuel cells must be provided with reactant gases for their operations. Fuel gases such as hydrogen or producer gas from the gasification of solid carbonaceous material can be employed. In addition, an oxidant gas such as oxygen or air must also be provided for reaction opposite the fuels. The manifolds carrying these reactant gases must be electrically insulated from the fuel cell stacks and connected to the stacks in a leak type manner. The high temperature and corrosive environment of molten carbonate fuel cells present difficult problems in providing these manifold connections. A particular difficult situation occurs when the sealing medium has a different coefficient of thermal expansion than that of the reactant gas manifold, plenum or the fuel cell stack.
Therefore it is an object of the present invention to provide an electrical insulator and sealing arrangement for use between a reactant gas plenum and a fuel cell stack.
It is a further object to provide an electrical insulator and seal capable of expanding and contracting consistent with the thermal expansion and contraction of the reactant gas plenum and fuel cell stack.
It is a further object to provide a gas seal between a reactant gas plenum and fuel cell stack which accommodates thermal expansion and contraction with minimum lateral movement of sealing surfaces.
One other object is to provide a reactant gas plenum seal that minimizes gas leakage resulting from thermal cycling of the fuel cell stack.
In accordance with the present invention, a combination electrical insulator and gas seal is provided for use between a reactant gas plenum and a stack of fuel cells within a fuel cell generator module. The combination insulator and seal includes a plurality of electrically insulative segments including segments with angular portions and segments with elongated portions arranged with ends in near abutment to form a closed frame between the reactant gas plenum and the fuel cell stack. Slidable splines are provided for connecting adjacent segments together in the frame configuration. Sealing surfaces are provided on opposite faces of the frame for engaging the reactant gas plenum walls and the fuel cell stack to minimize gas leakage from the plenum.
In more specific aspects of the invention, the spline connections between adjacent segments include keys which extend across the thickness of the electrically insulative segments and engage the sealing surfaces at the opposite faces of the frame. The spline keys slidably fit into slots defined between forked tines in adjacent end portions of the segments to form a labyrinth path minimizing gas leakage.
The seal and insulating frame is illustrated of rectangular shape consistent with rectangular adjacent portions of the gas plenum and fuel cell stack. The frame includes at least one slidable spline connection in each of the four sides such that expansion and contraction of the gas plenum walls and fuel cell stack can be faithfully tracked with minimum lateral motion across the sealing faces of the frame. This is of considerable importance and permits advantageous selection of the electrically insulated frame of a material having a substantially different coefficient of thermal expansion and contraction than that of the members to which it seals.